Technical Field
This Patent Disclosure relates generally to driver circuits for driving capacitive-load lines, such as mutual capacitance touch screens.
Related Art
A mutual capacitance touch screen is an example of a system requiring driving a capacitive load. The screen includes x/y (row/column) lines, with x-line drivers and y-line sense amps. Each x-line is characterized by a line-capacitance load.
FIGS. 1A and 1B illustrate a mutual capacitance touch screen with row/column (x/y) electrodes/lines, including line drivers and y-line sense amps.
One or more line drivers sequentially drive each line capacitance. Each driver output is a sinusoid voltage signal. Switch between multiple drivers to switch rows/columns on the display.
Touch systems commonly perform continuous/frequent scans to detect and respond to touches. This continual scanning operation consumes energy, especially for systems that need to monitor the panel for touches even when the display backlight is shut off.
One common approach to line driving is to use a boost converter to generate a high voltage rail and then to use class AB amplifiers to drive sinusoidal stimulation. That is, boost efficiency (which is relatively higher) is followed with the amp efficiency (which is relatively lower).
In addition, these line driver configurations require an array of driver ICs. Signal power is dissipated driving the line capacitance (fCV2). In addition, power is dissipated at the display capacitors.
In addition, line drivers need to support high-voltage signals. Design becomes complicated with low-cost deep-submicron CMOS technologies. High-voltage design trade-offs can degrade signal linearity performance.
While this Background information references wireless base station application, the Disclosure in this Patent Document is not limited to such applications, but is more generally directed to direct conversion wireless architectures.